Methyl methacrylate polymer laminated to a polyvinyl butyral by means of a silicic adhesive



Patented Mar. 25, 1947 UNITED STATE METHYL METHACRYLATE POLYMER LAMI- NATED TO A POLYVINYL BUTYRAL BY MEANS OF A SILICIC ADHESIVE Maurice L. Er'nsberger and Paul Swithin Pinkney, Wilmington, Del., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a

corporation of Delaware Application April 22, 1943, Serial No. 484,076

(on. ra -139) No Drawing.

8 Claims.

This invention relates to adhesives for joining plastics and, more particularly, relates to polysilicic acid esters as adhesives for joining solid, oxygen-containing, organic polymers.

The increased use of organic polymeric materials in recent years in a constantly expanding number of applications has led to new demands on the manufacturers of adhesives. When different polymers are used in the same article, they must often be joined together adhesively. Many polymers, such as methyl methacrylate polymer and polyvinyl butyral resin, are surprisingly difficult to stick together. In many instances it is particularly diflicult to obtain a joint between two polymers which will stand up under varied conditions of temperature, humidity and light,

mers. A more particular object is to provide a process of laminating sheets of plastic normally diflicult to adhere to each other. A specific ob-' ject is to-provide an improved adhesive for joining methyl methacrylate polymer to polyvinyl butyral resins. Other objects will be apparent from the description of the invention given hereinafter.

The above objects are accomplished accordin to the present invention by the use as an adhesive for joining solid, oxygen-containing, organic polymers, of an acid polysiliclc acid ester dissolved in an organic solvent. By the term acid polysilicic acid ester is meant a polysilicic acid ester containing --OH groups attached to Si, the normal meaning of that term.

The invention iscarried out by applying a thin film of a solution of an acid polysilicic acid ester in an organic solvent to the surfaces of the polymers to bejoined and pressing these surfaces together firmly until they are securely adher-ed, the length of time required for this vary-.

:ing inversely with the temperature employed.

- Preferably the solvent vehicle of the acid polysilicic acid ester adhesive composition which vehicle may be a single organic solvent or a mixture of two or more, comprises a volatile solvent and is characterized not only by being a solvent for the acid polysilicic acid ester but also by having a softening or, even better, a solvent action on the surfaces of the polymers to be joined. When the adhesive composition contains a volatile solvent, the iilm applied to the surfaces of the polymers is allowed to dry somewhat but A further object is to provide a process of joining such poly-- 2' before the fllm has dried tack free the surfaces to be joined are pressed together.

Solutions of acid polysiliclc acid esters suitable for use in this invention may be prepared by contacting dissolved polysiliclc acids with an esterifying agent such as a monohydric alcohol and removing water from the resulting solution as described in U. S. patent application Serial No. 439,549, filed April 18, 1940, in the name of Joseph S. Kirk and assigned to the assignee of the present application.

The more detailed practice of the present invention is illustrated by the following examples which show the use of acid polysiliclc acid esters as adhesives for joining various solid, oxygen mixture of volatile solvents one of which is a solvent for the organic polymers. In Example 3 the adhesive of Example 1 is used to join methyl methacrylate polymer to several additional polymeric materials. In Example 4 an ethanol solution of partially esterified polysiliclc acids is used to join cellulose derivatives to vinyl polymers.

0 In Example 5 a solution of partially esteriiied polysiliclc acids similar to that used in Example z is used to join cellulose acetate to other polymeric materials. All parts are given herein by weight unless otherwise specified. 1

Example 1 A tributyl phosphate solution of polysiliclc acids partially esterified with butanol is prepared as follows: An aqueous solution of polysillcic acids is prepared by adding 900 parts of a 15.5% solu tion of sodium silicate (SiOzZNazO=3.25:1 by weight) to 860 parts of a vigorously stirred solution oi. '7 sulfuric acid over a period of ten minutes. To the resulting solution, 196 parts of tri butyl phosphate and 460'parts or sodium chloride are added. Stirring is continued for one hour and then th mixture is allowed to stand for one hour. The upper, tributyl phosphate layer.

is separated, centrifuged, and dried over anhydrous sodium sulfate. The yield of clear, amber coated on both sides with the same solution. The

coated polyvinyl butyral resin is placed between the coated methyl methacrylate polymer surfaces and the three layers are pressed together at 150 C. for fifteen minutes under apressure of 500 lbs./sq. in. A clear seal is obtained. Although a .22 caliber pistol bullet fired through the laminated sheet at room temperature causes the layer of methyl methacrylate polymer penetrated first to shatter and separate from the polyvinyl butyral interlayer, the other layer of methylmethacrylate polymer remains stuck to the interlayer.

Example 2 A predominantly butanol solution or polysilicic acids which have been partially esterified with butanol is prepared as follows from the tributyl phosphate solution described in Example 1. One volume of the tributyl phosphate solution of partially esterified polysilicic acids is diluted with 1 volume 01' methanol and 2.5 volumes of benzene is added rapidly with stirring. The methanol solution of partially esterified polysilicic acids which separates as a lower layer when the mix- .ture is allowed to stand for fifteen minutes contains 50% to 60% S102. It is separated and dissolved in a mixture of butanol and acetic acid. The final solution contains 0.5% S102 and 20% acetic acid.

Two sheets of cast methyl methacrylat polymer are coated on one side with the butanolacetic acid solution of. acid polysilicic acid esters. A sheet of plasticized polyvinyl butyral resin is coated on both sides with the same solution. After the coatings have dried for fifteen minutes, the coated polyvinyl butyral resin is placed between the coated methyl methacrylate polymer surfaces, and the three layers are pressed together at 150 C. for fifteen minutes under a pressure of 500 lbs./sq. in. A clear seal is obtained. A .22 caliber pistol bullet shot through the laminated sheet at room temperature leaves a round hole with shattered edges and several long breaks in the layers of methyl methacrylate polymer. Nomore than a small wedge (a minor part of v the whole sheet) of methyl methacrylate polymer separates from the polyvinyl butyral interlayer.

The greater part ot-the laminated sheet remains one coherent piece alter the shot.

Example 3 The-tributyl phosphat solution of butyl acid polysilicates described in Example 1 is used as an adhesive in the lamination of sheets of each of the following polymeric materials between sheets of cast methyl methacrylate polymer.

((1) Ethylene/vinyl acetate interpolymer in which the ratio of ethylene to vinyl acetate is methyl methacrylate polymer and to both sides of the interlayer polymer. The lamination is carried out at 140 to 160 C. for ten minutes, under a pressure or 50 lbs. to 200 lbs/sq. in. In all cases the acid polysilicic acid esters provide a strong bond between the methyl methacrylate polymer and the polymer used as interlayer. Better adhesion is obtained with the 8:1 ethylene/vinyl acetate interpolymer than with the 25:1 ethylene/vinyl acetate interpolymer.

Example 4 A predominantly ethanol solution of partially esterified polysilicic acids is prepared by dissolving the concentrated methanol solution of partially esterified polysilicic acids described in Example 2 in sufficient ethanolto lower the concentration of S102 to 5% byweight. This solution is used in :the same manner as the solution of Example 3 as an adhesive in the lamination of a sheet of cellophane between sheets of unplasticized cellulose acetate, a sheet of cellophane between sheets of cast methyl methacrylate polymer, and a sheet of polyvinyl butyral resin between sheets of ethyl cellulose plasticized with dibutyl phthalate (12% based on the weight of ethyl cellulose). The coated sheets are pressed together before the acid polysilicic acid ester film has dried to a tackfree stage. They are subjected to pressures up to 2,500 lbs./sq. in. at temperatures from C. to C. for five to seven minutes. In all cases the acid polysilicic acid esters provide a strong bond between the laminated sheets. I

Example 5 The acid polysilicic acid ester solution described in Example 4 is diluted with ethanol and acetic acid to obtain a solution containing 3% S102 and 10% acetic acid. It is used in the same manner as the solution described in- Example 4, as an adhesive for laminating between sheets of unplasticized cellulose acetate, sheets of (a) polyvinyl alcohol, (b) an interpolymer obtained by interpolymerization of 1 mol of ethanolvamine, 1.75 mols of ethylene glycol, and 2.75 mols of adipic acid, and (c) an interpolymer obtained by interpolymerization of hexamethylenediammonium adipate, hexamethylenediammonium sebacate, and caprglactam. The laminations are carried out at 130 C. to C. for five to seven minutes under pressures up to 2,000 lbs/sq. in. In all cases the acid polysilicic acid esters provide a strong bond between the cellulose acetate and theinterlayer' polymer.

It will be understood that the above examples are merely illustrative and that the present invention broadly comprises the use of acid polysilicic acid esters dissolved in an organic solvent as an adhesive for joining solid, oxygen-containing, organic polymers. In general, any organic solvent-soluble acid polysilicic acid ester is effective to a greater or less extent as an adhesive for Joining any solid. oxygen-containing, organic polymers. 1

The term "oxygen-containing organic polymer as used herein is intended to include polymers which contain more oxygen than would normally trated by .the .results obtained with ethylene/vinyl acetate interpolymers in Example 3.

The oxygen in the organic polymer may be present in any of a variety of functional groups including ether, acid, ester, amide, anhydride, alcohol, ketone, and aldehyde groups. Thus, any one of the following polymers can be joined to itself or any of the others with the adhesive compositions of the present invention: coumarone resins; phenol-aldehyde resins; aldehyde resins; furfural resins; ketone resins; urea-formaldehyde type resins including thiourea-formaldehyde, melamine-formaldehyde and dicyandiamide-formaldehyde resins; sulfonamide-aldehyde resins: natural resins and their esters including rosin, shellac, and ester gum; condensation polyester resins including resins obtained from polyhydric alcohols and polybasic acids, and from hydroxyacids; polyamide resins; mixed polyester-polyamide resins; polyether resins; polyvinyl ethers; polyvinyl esters: polyvinyl alcohols; polyvinyl acetals; amides, and the like; cellulose and its derivatives including wood, cellophane,, and cellulose esters and ethers; and proteins, such as casein, zein, and soybean protein. These may be modified with any of the usual modifying agents including plasticizers, pigments, fillers, dyes, and materials which combine chemicallywith the polymer ingredients either during formation of the polymer or during an after-treatment. Thus, copolymers, interpolymers, and mixtures of polymers which comprise at least one oxygen-containing compound in chemical-combination with the polymer constituents are suitable for use with the adhesive of the present invention.

In addition to the acid polysilicic acid esters prepared as described in the examples, acid polysilicic acid esters prepared by any other processes are suitable for use in thisinvention. These include acid polysilicic acid esters prepared as described in the following references: the above referred to application of Joseph S. Kirk; U. S. application Serial No. 439,548, filed April 18, 1942, by Ralph K. Iler and Joseph S. Kirk, also assigned to the .assignee of the present application; U. 'S. 1,809,755; Ger. 568,545; and Ger. 696,814. The formation of a strong durable bond appears to depend on the ability of the polysilicic acid ester to polymerize further until a highly polymeric structure results. Therefore, it is necessary that it contain free silicic acid hydroxyl groups, which make possible the formation of high polymers through condensation. It may be desirable in some cases to prepare the acid polysilicic acid ester from a neutral polysilicic acid ester in situ by adding a suitable amount of water to the ester solution just before application; It is much preferred that the adhesive composition contain insuific'ient water to completely hydrolyze the polysilicic.acid ester, since on complete hydrolysis of a silicic acid ester, a siliclc acid gel or even silica is formed. These do not give a satisfactory adhesive bond.

' The acid polysilicic acid esters may vary in molecular weight from esters containing only two silicon atoms per molecule to those whose molecules are of colloidal dimensions and whose sols are approaching the gel state. In general. esters of relatively low molecular weight are preferred since they are more soluble and more compatible with organic materials than are the relatively high molecular weight esters. Thus they tend to penetrate the surfaces of the organic polymers and become more strongly anchored to them.

The acid polysilicic acid esters may vary also in the ratio of silicic acid ester groups to silicon atoms from 1:60 or less to 1:1 or more. Although the solubility of the ester in organic solvents and its compatibility with organic polymers increase with increase in degree of esterification of the polysilicic acid, the ester tends to polymerize more readily at lower temperatures and in a shorter time (i. e., it forms an adhesive bond under milder conditions) as the degree of esterification is decreased. A ratio of silicic acid esterigroups to silicon atoms of from 1:30 to 1:4

- is preferred. The optimum degree of esterificapolyacrylic acids, anhydrides, esters,

' and molecualr weight. The ester should, of

tion for each particular applicationcan readily be determined by a few preliminary tests.

The alcoholfrom which the acid polysilicic acid ester is derived may be primary, secondary, or tertiary, aliphatic or aromatic, cyclic or alicyclic, monoor polyhydric, saturated or unsaturated, and straight-chain or branched-chain. It may contain additional functional groups provided "such groups do not affect the stability of the acid polysilicic acid ester. Suitable functional groups include ether, halide, mercaptamsulfide, ketone, ester, amide, nitro, and nitrile groups. In some cases acid polysilicic acid esters containing such groups may be superior to unsubstituted esters in solubility in certain organic solvents and compatibility with certain polymers. The alcohol from which the acid polysilicic acid ester is derived may vary in chain length from 1 to 8. or more carbon atoms. Although the higher chain lengths are advantageous from the point of view of the solubility of the ester in organic solvents and, within limits, its compatibility with polymers, the short-chain esters, derived from alcohols containing less than'fi carbon atoms, such as methyl, ethyl, propyl, or butyl acid polysilicates are generally preferred since they tend to form an adhesive bond under milder conditions than do the longer chain esters.

The choice of the solvent from which the acid polysilicio acid ester is applied depends on a number of variables. One is the solubilityof the acid polysilicic acid ester, which varies with degree of esteriflcation, nature of esterifying groups,

course, be soluble in the solvent used. Another variable is the solubility of the polymer. It is preferable, although generally not necessary, to include in the acid polysilicic acid ester solution a liquid which will soften, or, even better, dissolve the surface polymer. Better anchorage of the highly,polym,eric silicic acid ester structure to the polymer surface is obtained in this way; Organic polymers varywidely, of course, in their solubllities, but in most cases suitable solvents or swelling agents are well known to those who are at all familiar with the resin field. In most cases a mixture of solvents including both a relatively volatile liquid and a solvent for the organic polymer is preferable. Solvents which may be found useful in this application include alcohols, ketones, esters of organic or inorganic acids, ethers, amides, and acids. Amines are not ordinarily suitable since they cause rapid gelato be joined or other polymers, to the acid polysilicic acid ester solution. The polymer added to the adhesive solution should preferably be compatible with the polymers to be joined.

It may in some cases be desirable to pretreat 8,418,018 V p 7 I 8 I the polymer surfaces which are to be Joined. dimensions of the objects which are being Joined Thus they may be softened or even made tacky is undesirable, temperatures and pressures which by use of a solvent before the adhesive composiwill cause the polymers to flow must be avoided.

tion is applied. Such pretreatment assists pene- When the relatively non-volatile liquid compotration of the acid polysilicic acid ester into the nent of the adhesive composition is not-rapidly polymer surface and leads to formation of a absorbed by one or-both of the polymers, use of stronger bond. excessively high temperatures will sometimes lead The acid polysilicic acid ester is preferably to bubble formation, which is detrimental to adapplied to the surface of the polymers which heslon as well as appearance. Since the optimum are to be joined in the form of a solution in a 10 as well as the permissible conditions of tempersuitable solvent as disclosed above. The solution t e a d P e depend one. ber of factors,

may be applied in any suitable manner, such-as it is often desirable to carry out pre by spraying, dipping, brushing, flowing, or using experiments on which to base selection of the cona doctor knife or applicator roll. The thickness ditions to be used in each particular case,

of thefilm of ester and nonvolatile solvent can The time required for formation of the adhesive be varied by use of a volatile solvent in varying bond decreases with increase in the temperature amounts. The concentration of acid polysilicic m y vIt lly decreases also Withla deacid ester in the solution on an S102 basis may c ase in the de ree of e ter flcation o th po yvary from 0.1% or lower to 30% or higher, prefl l acid employed. It also depends, of course,

erably from 0.5% to 15%. When the surfaces of 011 e Other o p n t of t ad e o the polymers to be joined are smooth, the more position and on the nature of the Po y rs bedilute solutions are usually satisfactory; when the tween which the d is to e formeds a ly polymer surfaces are rough, the more concenfrom e to fifteen mmutes is $umcient.'a1th0u8h trated solutions are preferable. The optimum at relatlvely low t peratures a period 01 Several proportions of acid polysilicic acid ester, volatile hours y qsolvent, and relatively non-volatile polymer 501- The s ve f he present invention is vent in the adhesive solution depend on the naadapte? Jolhmg polymers in a wide variety ture of each ingredient of the solution as well as appllcatiohs- The J' g of sheets of polymer on the ol mer to which it is to be applied and together to a laminated st ucture is one immust usually be determined for each particular Portant speclfie use Of s ad esive which is also case by preliminary tests. It may often be desiradapted for joining maseive P s of polymer in able, when the polymers to be joined differ widely the manufacture of venous artielesi the in their solubility characteristics, to coat one adhesive may be used to t a surface f a with an acid polysilicic acid ester solution which P r a d a film of a t P lymer may then differs widely in composition from that used to be deposited thereon y rushi spra inc. or coat the other polymer. In some instances it the like. innumerable uses of this adhesive will may be sufficient to coat only one of the surfaces be OPViOUS to those Skilled n the artto be joined. Italso may be desirable in some An a tage of the present invention is that it cases to apply the second polymer from solution. Pr vid s a practical and economical means of When the adhesive solution contains a volatile 4o nin lid. oxy i in or anic po solvent, it is usually preferable to allow time after mere t each ot th strong bond. A further application of the solution for most of the volatile a tage is that the pr n aiihesh'e can be solvent to evaporate. However, particularly used t j transparent Po y e s S nce it rewhen the degree of esterification of the polysilicic sults in a transparent film at the joint; this is acid is low, polymerization proceeds rapidly once P r icularly valuable with respect to the manut solvent has evaporated and hen b th of th facture of transparent laminated sheet structures. polymer surfaces to be joined are coated with Another advantag o t P ese t ve tion is the adhesive, it is important that the surfaces be that it gives rise to a bond between two polymers pressed together before the. acid polysilicic acid which 15 substantially unaffected y ed 0 nd!- ester has polymerized completely. For this reason 60 tions of temperature. humidity, and light, and is the polymer surfaces should preferably still be not weakened with the passa e of time.

tacky when they are pressed together. As many apparently widely different embodi- During formation ofthe adhesive bond between ments of this invention may be made without dethe polymers, the polymer surfaces must be held parting from the spirit and scope thereof, it is firmly against each other. For best results, suiii- 'to be,understood that the invention is not limited cient pressure must be used to obtain good contact to the Sp c fic embodiments thereof except 8 over the whole surface area. If the surfaces are defined in the appended claims.

uneven, pressures of 3,000 lbs/sq. in. or more may We claim:

be necessary. 1. A laminated article comprising a sheet of Application of heat to the polymers assists in et y met fl rylate pol m r an a Sheet of a the formation of a strong bond between them. polyvinyl buty l esi Said Sheets being Heat helps volatilize the remaining volatile soljoined t e y an adhesive compris g an vents and accelerates the polymerization of the acid polysilicic acid ester.

acid polysilicic acid esters. It also increases the *2. An article comprising a piece of methyl solubility of the polymer in any solvent which the methacrylate polymer and a piece of a polyvinyl adhesive composition may contain. The softening butyral resin joined together, said pieces having eifect of heat on thermoplastic polymers makes been joined together by coating at least one face it easier to obtain good contact between the polyof one of said pieces with a, solution of an acid mer surfaces at relatively low pressures. The I po y eeid e an anic ent and temperature used may vary from room temperpressing the two pieces together with the coated ature to 200 C. or higher. Temperatures of from surface of oneof said pieces adjacent to a face 50 C. to 150 C. are usually preferred. Discretion of the other of said pieces.

must be used in the application of heat and 3. An article comprising a piece of methyl pressure, especially when the polymers are thermethacrylate polymer and a piece of a polyvinyl moplastic. For example, when change in the butyral resin joined together, said pieces having been joined together by coating at least one face of one of said pieces with a solution of an acid silicic acid ester in a solvent vehicle comprising an organic solvent having at least a softening effect on said piece, and pressing the two pieces together with the coated surface of one of said .pieces adjacent to a face of the other of said pieces. I

4. An article comprising a piece of methyl methacrylate polymer and a piece of a polyvinyl butyral resin joined together by an adhesive comprising an acid polysilicic acid ester.

5. Process of joining a piece of methyl methacrylate polymer and a piece of a polyvinyl butyral resin which comprises coating at least one face of one of said pieces with a solution of an acid polysilicic acid ester in which the ratio of silicic acid ester groups to silicon atoms is from 1:30 to 1:4, in an organic solvent and pressing the two pieces togetherwith the coated surface of one of said pieces adjacent to a face of the other of said pieces.

6. Process of joining a piece of methyl methacrylate polymer and a piece of a-polyvlny1 butyral resin which comprises coating at least one face of one of said pieces with a solution of an acid polysilicic acid ester of an alcohol containing less than 6 carbon atoms and in which ester the ratio of silicic acid ester groups to silicon atoms is from 1:30 to 1:4, in an organic solvent and pressing the two pieces together with the coated surface of one of said pieces adjacent to a face is from 1:30 to 1:4, in an organic solvent and pressing the two pieces together with the coated surface of one of said pieces adjacent to a face of I the other of said pieces.

8. Process of joining a piece of methyl'methacrylate polymer and a piece of a. polyvinyl butyral resin which comprises coating at least one face of one of said pieces witha solution of an nbutyl acid polysilicate in which the ratio of silicic 10 acid ester groups to silicon atoms is from 1:30

to 1:4, in a solvent vehicle comprising tributyl phosphate, and pressing the two pieces together with the coated surface of one of said pieces adjacent to a face of the other of said pieces.

MAURICE L. ERNSBERGER. PAUL SWITHIN PINKNEY.

REFERENCES CITED 2 The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,809,755 King June 9, 1931 2,258,218 Rochow Oct. 7, 1941 2,317,891 Dennison 'Apr. 27, 1943 FOREIGN PATENTS Number 1 Country Date 157,688 Austrian Jan. 10, 1940 OTHER REFERENCES Andreanou (1) Org. Chem. Industry, U. S. 8.

6, pages 203-7 (1939).

Andreanou (2), Jour. Gen. Chem. U. S. S. R. 8.

pages 1255-62 (1938).

(Copies of the above pages from the respective publications are available .in Division of this 

